A method for removing impurities accumulated in a scrubbing fluid in a flue gas scrubber and effluents from the scrubber. The flue gases are scrubbed with a scrubbing fluid that includes a calcium-containing absorbent. The scrubbing fluid containing gypsum and other impurities and produced in the scrubber is discharged from the scrubber. The gypsum is separated from the scrubbing fluid. To the scrubbing fluid is added an auxiliary agent, by the effect of which the impurities accumulated in the scrubbing fluid are removed with the gypsum and the moisture content of the gypsum to be separated from the scrubbing fluid is increased.